Spermatogenesis is an androgen-dependent process and androgen-binding protein (ABP), a secretory product of Sertoli cells, is considered a mediator of androgens action on the developing germ cells. However, ABP's precise mode of action is not known. In order to understand the functions of ABP and, in a broader sense, the role of androgens in the control of spermatogenesis, we have studied transgenic mice expressing high amounts of ABP. These animals show progressive abnormalities of spermatogenesis and an eventual loss of fertility. In order to explain this finding, we hypothesize that the chronic overproduction of ABP changes the balance between proliferation and degeneration (apoptosis) of germ cells by changing the steroid hormone milieu within the seminiferous tubules. This may involve not only testosterone, but also is biologically active intratesticular metabolites dihydrotestosterone and estradiol. To test the above hypothesis, we propose to determine the effects of excess ABP produced in the transgenic animals on (1)-- testicular levels of testosterone, dihydrotestosterone, estradiol, and the androgen and estrogen receptors. Specific radioimmunoassays, immunocytochemistry, and in situ hybridization will be used to achieve this goal. (2)--the kinetics of germ cell proliferation and apoptosis preceding and during the decline in spermatogenesis. Flow cytometry and morphometric analysis will be used after specific labeling of both proliferating and apoptotic cells. Apoptosis will be detected by in situ end labeling of fragmented DNA and by gel electrophoresis. (3)-- the expression of genes regulating germ cell proliferation and apoptosis. Gene expression will be analyzed before and during the decline in spermatogenesis by immunocytochemistry, in situ hybridization, in situ PCR, and Northern blot analysis. These studies will lead to a better understanding of the regulation of spermatogenesis and of some forms of male infertility; they may also reveal potential new targets for male contraception.